Animal feeding studies (mice) are under way to evaluate the effect of type of fat (degree of saturation) and quantity of fat in the diet (two levels) on the incidence of spontaneous and induced cancer in mice. Additional studies will test the effect of a diet high in trans isomers and high in triene content on cancer incidence. High fat diets will also be fed with and without an antioxidant to evaluate this parameter. Dietary substitutions are made on an isocaloric basis so that per calorie consumed, all other nutrient intakes will be constant. Ancillary studies will be done to evaluate the effects of these dietary manipulations on structure and functions of cellular components such as membranes, mitochondria and microsomes.